using System.Diagnostics;
using System.Globalization;
using System.Text.RegularExpressions;
using Windows.Storage;

namespace ServerMonitorManager_Desktop;

public sealed record ServerMetrics(
    string Hostname,
    double CpuPercent,
    long MemoryUsedKb,
    long MemoryTotalKb,
    long DiskUsedKb,
    long DiskTotalKb,
    TimeSpan Uptime,
    TimeSpan Latency);

public sealed partial class SshMonitorService
{
    private const string KeyFileName = "server-monitor-manager-ed25519";

    public async Task<string> EnsureKeyPairAsync(CancellationToken cancellationToken = default)
    {
        var keyFolder = await ApplicationData.Current.LocalFolder.CreateFolderAsync(
            "ssh",
            CreationCollisionOption.OpenIfExists);
        var privateKeyPath = Path.Combine(keyFolder.Path, KeyFileName);
        var publicKeyPath = privateKeyPath + ".pub";

        if (!File.Exists(privateKeyPath) || !File.Exists(publicKeyPath))
        {
            var arguments = new[]
            {
                "-q", "-t", "ed25519", "-a", "64", "-N", string.Empty,
                "-C", "server-monitor-manager", "-f", privateKeyPath
            };
            await RunProcessAsync(ResolveOpenSshTool("ssh-keygen.exe"), arguments, cancellationToken);
        }

        return (await File.ReadAllTextAsync(publicKeyPath, cancellationToken)).Trim();
    }

    public async Task<ServerMetrics> QueryAsync(
        ServerProfileData profile,
        CancellationToken cancellationToken = default)
    {
        var stopwatch = Stopwatch.StartNew();
        var output = await RunRestrictedCommandAsync(profile, "metrics", cancellationToken);
        stopwatch.Stop();

        var values = output
            .Split(['\r', '\n'], StringSplitOptions.RemoveEmptyEntries)
            .Select(line => line.Split('=', 2))
            .Where(parts => parts.Length == 2)
            .ToDictionary(parts => parts[0], parts => parts[1], StringComparer.Ordinal);

        var cpuCount = ReadLong(values, "CPU_COUNT", 1);
        var load1 = ReadDouble(values, "LOAD1");
        var cpuPercent = Math.Clamp(load1 / Math.Max(1, cpuCount) * 100, 0, 100);
        var memoryTotal = ReadLong(values, "MEM_TOTAL_KB");
        var memoryAvailable = ReadLong(values, "MEM_AVAILABLE_KB");
        var diskTotal = ReadLong(values, "DISK_TOTAL_KB");
        var diskAvailable = ReadLong(values, "DISK_AVAILABLE_KB");

        return new ServerMetrics(
            values.GetValueOrDefault("HOSTNAME", profile.Name),
            cpuPercent,
            Math.Max(0, memoryTotal - memoryAvailable),
            memoryTotal,
            Math.Max(0, diskTotal - diskAvailable),
            diskTotal,
            TimeSpan.FromSeconds(ReadLong(values, "UPTIME_SECONDS")),
            stopwatch.Elapsed);
    }

    public async Task<string> RunRestrictedCommandAsync(
        ServerProfileData profile,
        string command,
        CancellationToken cancellationToken = default)
    {
        ValidateProfile(profile);
        if (!SafeRestrictedCommandRegex().IsMatch(command))
        {
            throw new InvalidOperationException("Некорректная команда управления Mesh.");
        }

        await EnsureKeyPairAsync(cancellationToken);
        var localFolder = ApplicationData.Current.LocalFolder.Path;
        var privateKeyPath = Path.Combine(localFolder, "ssh", KeyFileName);
        var knownHostsPath = Path.Combine(localFolder, "ssh", "known_hosts");
        var target = $"{profile.User}@{profile.Host}";
        var arguments = new[]
        {
            "-i", privateKeyPath,
            "-p", profile.Port.ToString(CultureInfo.InvariantCulture),
            "-o", "BatchMode=yes",
            "-o", "ConnectTimeout=8",
            "-o", "IdentitiesOnly=yes",
            "-o", "StrictHostKeyChecking=accept-new",
            "-o", $"UserKnownHostsFile={knownHostsPath}",
            target,
            command
        };
        return await RunProcessAsync(
            ResolveOpenSshTool("ssh.exe"),
            arguments,
            cancellationToken);
    }

    private static void ValidateProfile(ServerProfileData profile)
    {
        if (!SafeHostRegex().IsMatch(profile.Host))
        {
            throw new InvalidOperationException("Некорректный адрес сервера.");
        }

        if (!SafeUserRegex().IsMatch(profile.User))
        {
            throw new InvalidOperationException("Некорректное имя SSH-пользователя.");
        }

        if (profile.Port is < 1 or > 65535)
        {
            throw new InvalidOperationException("SSH-порт должен быть от 1 до 65535.");
        }
    }

    private static async Task<string> RunProcessAsync(
        string fileName,
        IEnumerable<string> arguments,
        CancellationToken cancellationToken)
    {
        var startInfo = new ProcessStartInfo
        {
            FileName = fileName,
            UseShellExecute = false,
            CreateNoWindow = true,
            RedirectStandardOutput = true,
            RedirectStandardError = true
        };
        foreach (var argument in arguments)
        {
            startInfo.ArgumentList.Add(argument);
        }

        using var process = Process.Start(startInfo)
            ?? throw new InvalidOperationException($"Не удалось запустить {Path.GetFileName(fileName)}.");
        var outputTask = process.StandardOutput.ReadToEndAsync(cancellationToken);
        var errorTask = process.StandardError.ReadToEndAsync(cancellationToken);

        try
        {
            await process.WaitForExitAsync(cancellationToken);
        }
        catch
        {
            if (!process.HasExited)
            {
                process.Kill(entireProcessTree: true);
            }
            throw;
        }

        var output = await outputTask;
        var error = await errorTask;
        if (process.ExitCode != 0)
        {
            throw new InvalidOperationException(
                string.IsNullOrWhiteSpace(error)
                    ? $"SSH завершился с кодом {process.ExitCode}."
                    : error.Trim());
        }

        return output;
    }

    private static string ResolveOpenSshTool(string fileName)
    {
        var systemTool = Path.Combine(
            Environment.GetFolderPath(Environment.SpecialFolder.System),
            "OpenSSH",
            fileName);
        return File.Exists(systemTool) ? systemTool : fileName;
    }

    private static long ReadLong(IReadOnlyDictionary<string, string> values, string key, long fallback = 0)
        => values.TryGetValue(key, out var value)
            && long.TryParse(value, NumberStyles.Integer, CultureInfo.InvariantCulture, out var parsed)
                ? parsed
                : fallback;

    private static double ReadDouble(IReadOnlyDictionary<string, string> values, string key)
        => values.TryGetValue(key, out var value)
            && double.TryParse(value, NumberStyles.Float, CultureInfo.InvariantCulture, out var parsed)
                ? parsed
                : 0;

    [GeneratedRegex("^[A-Za-z0-9._:-]{1,255}$", RegexOptions.CultureInvariant)]
    private static partial Regex SafeHostRegex();

    [GeneratedRegex("^[a-z_][a-z0-9_-]{0,31}$", RegexOptions.CultureInvariant)]
    private static partial Regex SafeUserRegex();

    [GeneratedRegex("^(metrics|mesh (nodes|links|status|connect [a-z0-9][a-z0-9-]{0,31} [a-z0-9][a-z0-9-]{0,31} (tcp|udp) [0-9]{1,5} [0-9]{1,6}|disconnect [a-z0-9][a-z0-9-]{0,31} [a-z0-9][a-z0-9-]{0,31} (tcp|udp) [0-9]{1,5}))$", RegexOptions.CultureInvariant)]
    private static partial Regex SafeRestrictedCommandRegex();
}